Characterization of New Carbosilane Liquid Crystalline Monomers and Dimers

Transcription

1 Characterization of New Carbosilane Liquid Crystalline Monomers and Dimers By Sarah Hosawi A thesis submitted to the Department of Chemistry In conformity with the requirements for the degree of Master of Science Queen s University Kingston, Ontario, Canada August, 2016 Copyright Sarah Hosawi, 2016

2 Abstract De Vries-like smectic liquid crystals exhibit low layer contraction of approximately 1% on transitions from the SmA to the SmC phase. These materials have received considerable attention as potential solutions for problems affecting liquid crystal displays using surfacestabilized ferroelectric liquid crystals (SSFLC). In SSFLCs, layer contraction of 7 10% is normally observed during the SmA to SmC phase transition. A study by the Lemieux group has shown that liquid crystals with nanosegregating carbosilane segments exhibit enhanced de Vries-like properties through the formation of smectic layers and by lengthening the nanosegregating carbosilane end-groups from monocarbosilane to tricarbosilane. This observed enhancement is assumed to be due to an increase in the cross-section of the free volume in the hydrocarbon sub-layer. To test this hypothesis, it is assumed that dimers with a tricarbosilane linking group have smaller cross-sections on time average. In this thesis, this hypothesis is tested through the characterization of new liquid crystalline monomers (QL39- n) and dimers (QL40-n) with 2-phenylpyrimidine cores and tricarbosilane end-groups and spacers, respectively. The thesis describes the synthesis of two homologous series of liquid crystals and their characterization using a variety of techniques, including polarized optical microscopy, differential scanning calorimetry and X-ray diffraction. The results show that the monomers QL39-n form a tilted SmC phase only, whereas the dimers QL40-n form an orthogonal SmA phase. These results are discussed in the context of our hypothesis. ii

3 Acknowledgements I would like to thank my supervisor, Dr. Bob Lemieux for his support, patience and guidance during this project. I would also like to thank all members of the Lemieux group, and Dr. Kirk Mulligan and Dr. Chris Schubert in particular, for their assistance and valuable suggestions. I would like to thank all of those individuals in the Chemistry Department who have helped me throughout my studies. In particular, I would like to thank Dr. Françoise Sauriol in the NMR facility, Dr. Jiaxi Wang in the mass spectrometry lab, and Kim Mackinder in the Science Store for their help. I would like to thank Carsten Müller and Prof. Frank Giesselmann of the University of Stuttgart for performing the X-ray scattering measurements reported in this thesis. Finally, I would like to thank my husband, Ibrahim for all his support and understanding, and my parents for their encouragement and support. I could not have completed this research project without their assistance. I would also like to thank Saudi Arabia scholarship program for their financial support during my graduate study. iii

4 TABLE OF CONTENTS ABSTRACT... ii ACKNOWLEDGEMENTS... iii TABLE OF CONTENTS... iv LIST OF FIGURES... vi LIST OF TABLES... xi ABBREVIATIONS... xii Chapter 1. Introduction Classification of Liquid Crystals Calamitic Mesophases The Nematic Phase (N) The Smectic A Phase (SmA) The Smectic C Phase (SmC) Chirality in Smectic C Phase Chiral Smectic C (SmC*) Phase-Ferrelectric Liquid Crystals SSFLC Display Technology Problems De Vries-Like Materials DeVries Diffuse Cone Model Low Orientational Order and High Lamellar Order Nanosegragation Examples of Known Carbosilane-Terminated de Vries-like Materials The Effect of Carbosilane Nanosegregation on de Vries-like Properties Hypothesis Test of Hypothesis iv

5 1.6 Project Outline References Chapter 2. 2-Phenylpyrimidine Monomeric and Dimeric Tricarbosilane Liquid Crystals Syntheses Mesophase Characterization X-ray Scattering Experiments Electro-Optic Response SmX phase Conclusions References Chapter 3. Experimental Syntheses and characterization General Materials Synthesis of QL39-n liquid crystal monomers Syntheses of QL40-n liquid crystal dimers References Chapter 4. Conclusions and Future Work Appendix 1. 1 H NMR Spectra of Novel Compounds Appendix 2. DSC Profiles of Liquid Crystals Appendix 3. Textures of liquid crystals by polarized microscopy v

6 LIST OF FIGURES Figure 1-1: Examples of calamitic, discotic, bent-core and polycatenar liquid crystals... 3 Figure 1-2: Examples of perfluorinated and organosiloxane liquid crystals... 3 Figure 1-3: 2-(4-Butoxyphenyl)-5-(octyloxy)pyrimidine a common calamitic liquid crystal and phase transition temperatures in C. 4 Figure 1-4: Schematic of phase transitions between crystalline, smectic C, smectic A, nematic (N), and isotropic liquid phases for a calamitic material as a function of temperature. 4 Figure 1-5: Structure of the nematic phase and characteristic Schlieren texture observed by polarized optical microscopy Figure 1-6 Structure of the smectic A phase and characteristic fan and homoetropic textures observed by polarized optical microscopy Figure 1-7: Structure of the smectic C phase and characterictic broken fan and Schlieren textures observed by polarized optical microscopy... 7 Figure 1-8: Schematic representation of the McMillan model Figure 1-9: Schematic representation of the Wulf model....8 Figure 1-10: Schematic representations of symmetry elements of achiral SmC phase and SmC* phase after chiral doping...10 Figure 1-11: Schematic representations of macroscopic helical arrangement of SmC* phase in bulk material (left) and in surface-stabilized state (right) 10 Figure 1-12: Schematic representation of ON/OFF light shutter (+θ and θ directions) in SSFLC..11 Figure 1-13: (a) The SmA* phase in the bookshelf configuration. (b) the SmC*phase in the chevron configuration.. 12 Figure 1-14: A picture of zigzag defects in a SmC* phase vi

7 Figure 1-15: Schematic representation of the (a) rigid rod model and (b) diffuse cone model 14 Figure 1-16: Organization of the oligosiloxane-containing liquid crystals in the smectic Layer (ref. 4) Figure 1-17: Smectic layer spacing d/dac versus the reduced temperature T TAC for mesogens QL13-3, QL18-3, QL19-6, and QL28-6/6 (from ref. 18)..19 Figure 1-18: Orientational order parameter (S2) versus reduced temperature T TAC for mesogens QL13-3, QL18-3, QL19-6, and QL28-6/6 (from ref. 18)..20 Figure 1-19: Schematic representations the bulky size of the monocarbosilane end-group (left) and tricarbosilane (right) Figure 2-1: Polarized photomicrograph of QL39-6 monomer on cooling: SmC phase at 70 C..27 Figure 2-2: Polarized photomicrographs of QL40-6 dimer on cooling: (a) SmA phase at 91 C and (b) SmX phase at 74 C Figure 2-3: DSC profile for QL39-6 compound taken at 5 K/min scan rate. 28 Figure 2-4: DSC profile for QL40-6 compound taken at 5 K/min scan rate Figure 2-5: Phase transition temperatures for QL39-n monomeric series and QL40-n dimeric series measured via DSC upon heating at 5 K/min rate..29 Figure 2-6: Smectic layer spacing d versus reduced temperature T Tx for QL40-6 compound.32 Figure 2-7: Fully extended calculated model of QL40-6 dimer 32 Figure 2-8: 2D X-ray scattering patterns at T TAX = +15 K and T TAX = -10 K (left), and diffuse wide-angle scattering as function of azimuthal angle for QL40-6 at 70, 85 and 100 C (right). 33 vii

8 Figure 2-9: χ scan for the wide-angle and small-angle at Figure 2-10: Orientational order parameter S2 vs. temperature for QL40-6 compound...34 Figure 2-11: Polarization reversal current profiles for surface-stabilized films (4 µm) of (a) QL39-6 and (b) QL40-6 (in the SmX phase), both doped with the chiral mesogen QL32-6 (5 mol%), upon application of triangular AC voltage of 6 V/µm and 100 Hz Figure 2-12: Two polarization current peaks appear for smectic C antiferroelectric phase in response to triangular voltage waveform (ref. 6). 36 Figure Schematic representation of bulky size of tricarbosilane unit for dimer SmA phase.37 Figure A1-1: 400 MHz 1H NMR spectrum of QL Figure A1-2: 400 MHz 1H NMR spectrum of QL Figure A1-3: 400 MHz 1H NMR spectrum of QL Figure A1-4: 400 MHz 1H NMR spectrum of QL Figure A1-5: 400 MHz 1H NMR spectrum of QL Figure A1-6: 400 MHz 1H NMR spectrum of QL Figure A1-7: 400 MHz 1H NMR spectrum of QL Figure A1-8: 400 MHz 1H NMR spectrum of QL Figure A1-9: 400 MHz 1H NMR spectrum of QL Figure A1-10: 400 MHz 1H NMR spectrum of QL Figure A1-11: 400 MHz 1H NMR spectrum of QL Figure A1-12: 400 MHz 1H NMR spectrum of QL Figure A2-1: DSC profile for compound QL39-5 taken at a scan rate of 5K/min Figure A2-2: DSC profile for compound QL39-6 taken at a scan rate of 5K/min Figure A2-3: DSC profile for compound QL39-7 taken at a scan rate of 5K/min Figure A2-4: DSC profile for compound QL39-8 taken at a scan rate of 5K/min viii

9 Figure A2-5: DSC profile for compound QL39-7 taken at a scan rate of 5K/min Figure A2-6: DSC profile for compound QL39-10 taken at a scan rate of 5K/min Figure A2-7: DSC profile for compound QL40-5 taken at a scan rate of 5K/min Figure A2-8: DSC profile for compound QL40-6 taken at a scan rate of 5K/min Figure A2-9: DSC profile for compound QL40-7 taken at a scan rate of 5K/min Figure A2-10: DSC profile for compound QL40-8 taken at a scan rate of 5K/min Figure A2-11: DSC profile for compound QL40-9 taken at a scan rate of 5K/min Figure A2-12: DSC profile for compound QL40-10 taken at a scan rate of 5K/min Figure A3-1: Textures of compound QL39-5 observed by polarized microscopy on cooling: in the SmC phase at 42 C Figure A3-2: Textures of compound QL39-6 observed by polarized microscopy on cooling: in the SmC phase at 70 C Figure A3-3: Textures of compound QL39-7 observed by polarized microscopy on cooling: in the SmC phase at 68 C Figure A3-4: Textures of compound QL39-8 observed by polarized microscopy on cooling: in the SmC phase at 69 C Figure A3-5: Textures of compound QL39-9 observed by polarized microscopy on cooling: in the SmC phase at 66 C Figure A3-6: Textures of compound QL39-10 observed by polarized microscopy on cooling: in the SmC phase at 80 C Figure A3-7: Textures of compound QL40-5 observed by polarized microscopy on cooling in the SmA at 85 C on cooling (left) and the SmX phase at 70 C (right) (200X Magnification) Figure A3-8: Textures of compound QL40-6 observed by polarized microscopy on cooling in the SmA at 91 C on cooling (left) and the SmX phase at 74 C (right) (200X ix

10 Magnification) Figure A3-9: Textures of compound QL40-7 observed by polarized microscopy on cooling in the SmA at 90 C on cooling (left) and the SmX phase at 75 C (right) (200X Magnification) Figure A3-10: Textures of compound QL40-8 observed by polarized microscopy on cooling in the SmA at 95 C on cooling (left) and the SmX phase at 93 C (right) (200X Magnification) Figure A3-11: Textures of compound QL40-9 observed by polarized microscopy on cooling: in the SmA phase and the interfere SmA phase at 85 C (200X Magnification). 70 Figure A3-12: Textures of compound QL40-10 observed by polarized microscopy on cooling: in the SmA phase and the interfere SmA phase at 90 C (200X Magnification)...70 x

11 LIST OF TABLES Table 1-1: Liquid crystal layer dac spacings, orientational order parameter S2 and reduction factor R at T TAC = 10 K 20 Table 2-1: Transition temperatures and enthalpies of transition (kj mol -1, in parentheses) for QL39- n and QL40- n compounds xi

12 Abbreviations H Å Ac aq C2 calcd χd Cdv cm Cr d(tac) da dc DSC EI ESI Et Et2O EtOAc EtOH FLC h HPLC Enthalpy of transition Angstrom Acetyl Aqueous C2-symmetric conformer Calculated Mole fraction of the dopant de Vries coefficient Centimeter Crystalline Layer spacing at transition from SmA phase to SmC phase Layer spacing in sma phase Layer spacing in smc phase Differential scanning calorimetry Electron impact ionization Electrospray ionization Ethyl Diethylether Ethyl acetate Ethanol Ferroelectric liquid crystal Hours High performance liquid chromatography xii

13 HRMS I 2-PhP ipr ITO J kj LC LCD M Me MHz min mm mol mp MS N n High resolution mass spectrometry Isotropic 2-Phenylpyrimidine Isopropyl Indium-tin oxide Coupling constant KiloJoule Liquid crystal Liquid crystal display Molar Methyl Megahertz Minutes Millimeter Mole Melting point Mass spectrometry Nematic Director N* Chiral nematic NMR Ph Po POM Nuclear magnetic resonance Phenyl Reduced polarization Polarized optical microscopy xiii

14 PPh3 MgSO4 ppm Ps q R rt. sat SAXS SmA SmA* SmC SmC* SSFLC TC THF TOF V z (T) P Triphenylphosphine Magnesium sulfate Part per million Spontaneous polarization Tilt angle A figure of merit Room temperature Saturated Small-angle X-ray scattering Smectic A Chiral Smectic A Smectic C Chiral Smectic C Surface-stabilized ferroelectric liquid crystal Curie point Tetrahydrofuran Time of flight Volt Layer normal Chemical shift Chevron layer tilt angle Polarization power xiv

15 Chapter 1. Introduction Liquid crystals are materials whose properties lie between those of the conventional solid crystalline state and isotropic liquid state. At high temperatures, thermotropic liquid crystals are isotropic liquids; however, they undergo a phase transition into the liquid crystal phase when the temperature is decreased. Liquid crystals are unique and fascinating materials and have been extensively studied since their discovery in, Liquid crystal materials have strong potential for technological applications; one of the most important examples is the liquid crystal display (LCD), which is firmly reliant on the liquid crystal mixtures used. Although twisted nematic LCD have attained good commercial success, they have some problems with poor response and narrow viewing angles. Scientists have been able to solve those problems through their investigations of ferroelectric liquid crystals (FLCs) as an alternative technology. Commercial FLC mixtures usually have a chiral dopant combined with an achiral liquid crystal host that has low viscosity and a broad temperature range (vide infra). More recent studies have focused on so-called de Vries-like liquid crystals to solve the problems that decrease the quality of FLC applications 2. In recent years, liquid crystal dimers have been employed as model compounds for semi-flexible main-chain liquid crystal polymers 3. In this case, the term dimer refers to molecules that have two rigid mesogenic units connected via a flexible spacer such as an alkyl chain. The liquid crystal dimers can be divided into groups that are either symmetric or nonsymmetric; the former includes two identical mesogenic units, whereas the latter has two different mesogenic units. In this regard, liquid crystal dimers show interesting phase behaviors that significantly differ from those of conventional low-molar-mass liquid crystals 4. 1

16 This thesis focuses on the synthesis and characterization of new liquid crystal monomers and dimers with tricarbosilane end-groups and spacers, respectively, with the aim of clarifying the relationship between their structures and properties Classification of Liquid Crystals Liquid crystals are materials that exhibit the properties of both solids and liquids. Molecules that form liquid crystals are termed mesogens, and the term mesophase refers to the liquid crystal phase that is formed by these mesogens. In general, liquid crystals can be organized into two basic classes: thermotropic and lyotropic. In a thermotropic liquid crystal, materials form mesophases in response to temperature changes in the absence of solvent. Lyotropic liquid crystals, in contrast, require the addition of solvent to form mesophases that are responsive to both thermal and concentration changes. This thesis will focus on thermotropic liquid crystals. Typically, thermotropic liquid crystals are sub-classified depending on their molecular shape. They fall into four groups: calamitic, discotic, polycatenar, and bent-core, as shown in Figure 1-1. Calamitic liquid crystals consist of rod-shaped molecules that have rigid core units linked to flexible side chains. Discotic liquid crystals consist of disc-shaped molecules that have flat polyaromatic core units linked with multiple alkyl side chains. Polycatenar liquid crystals consist of brick- or lath-shaped molecules that have narrow rigid core units linked with multiple alkyl side chains. Bent-core liquid crystals consist of rod-like mesogens that are banana-shaped. Thermotropic liquid crystals can additionally be classified as either nonamphiphiles or amphiphiles 5. The group of liquid crystals shown in Figure 1-1 are nonamphiphiles, but the amphiphilic liquid crystals depend on differences in the compatibility 2

17 of their molecular parts to promote ordering by microsegregation. The organosiloxane and perfluorinated compounds shown in Figure 1-2 typify this group. Calamitic polycatenar Discotic Bent-core Figure 1-1. Examples of calamitic, discotic, bent-core and polycatenar liquid crystals. perfluorinated organosiloxane Figure 1-2. Examples of perfluorinated and organosiloxane liquid crystals. 3

18 1. 2 Calamitic Mesophases Calamitic liquid crystals are formed by rod-like molecules (mesogens). Generally, their structure contains a rigid aromatic core unit linked with one or two flexible side chains, as shown in Figure 1-3, allowing them to form a diverse range of liquid crystal phases as a function of temperature (Figure 1-4). There are two main classes of liquid crystal phases in calamitic mesogens: the nematic (N) and smectic phases. The N liquid crystalline phase shows only orientational order, whereas the smectic phases show both orientational and translational (lamellar) order. There are several smectic phases; the most important are the SmA and SmC phases, which have been used in display devices (vide infra). PhP1: phase sequence: Cr 58 SmC 85 SmA 95 N 98 I Figure (4-Butoxyphenyl)-5-(octyloxy)pyrimidine a common calamitic liquid crystal and phase transition temperatures in C 6. Figure 1-4. Schematic of phase transitions between crystalline, smectic C, smectic A, nematic (N), and isotropic liquid phases for a calamitic material as a function of temperature. 4

19 1.2.1 The Nematic Phase (N) Upon cooling from a completely disordered (isotropic) liquid, the N liquid crystalline phase is the first phase observed (Figure 1-5). In the N phase, the rod-like molecules are arranged in a random positional order, but the molecular long axes are all oriented along an axis termed the director, n. The orientation of the N phase can be described by an order parameter, S2, according to Equation (1.1) 7 : S 2 = 1 2 < 3 cos2 θ 1 > (1.1) where θ is the angle between the long axis of the molecules and the director n. In the N phase, the value of S2 is usually in the range , whereas S2 = 0 and 1 in the disordered liquid phase and the highly ordered crystalline phase, respectively. Figure 1-5: Structure of the nematic phase and characteristic Schlieren texture observed by polarized optical microscopy The Smectic A Phase (SmA) In the SmA phase, which appears upon further cooling from the N phase, the director n is parallel to the smectic layer normal z, as shown in Figure 1-6. The layers in SmA phases are not correlated with each other and the mesogens are free to rotate around their long axes 5

20 due to the short range positional order within each layer. As the orientational order of the SmA phase is typically greater than in the N phase, the parameter S2 usually exhibits a value of ~ 0.8. Under a polarized microscope, the SmA phase typically shows a focal conic (fan) texture and a homeotropic texture (dark regions). The homeotropic regions appear because the mesogens in the SmA phase are oriented perpendicularly to the glass slide, so no birefringence is exhibited. Figure 1-6: Structure of the smectic A phase and characteristic fan and homoetropic textures observed by polarized optical microscopy The Smectic C Phase (SmC) The SmC phase is closely related to the SmA phase, and it also shows orientational and translational order. However, in the SmC phase, the molecular orientation is uniformly tilted (oriented away from the normal). The mesogen orientation n is tilted with respect to the layer normal z by a tilt angle θ, as shown in Figure 1-7; θ is normally temperature dependent and increases with decreasing temperature. In general, the SmC phase is a tilted configuration of the SmA phase. The textures formed by the SmC phase are usually described as broken fan and Schlieren textures. 6

21 Figure 1-7: Structure of the smectic C phase and characterictic broken fan and Schlieren textures observed by polarized optical microscopy. The models proposed by McMillan and Wulf are the most commonly used to describe the origin of the molecular tilt in the SmC phase. The McMillan model, 8 proposed in 1973, postulated that mesogens exhibiting SmC phases have polar groups such as ethers groups in both side chains linked to the core. He suggested that the formation of the SmC phase arises from the coupling of the outboard dipoles from the polar functional groups. The model also suggests that, upon cooling from the SmA to the SmC phase, the rotational order around the director n increases because of the coupling of the outboard dipoles, which leads to an induced torque, observed as tilt, in the SmC (Figure 1-8). Figure 1-8: Schematic representation of the McMillan model. 7

22 However, there are some calamitic mesogens that show SmC phases without the coupling of outboard dipoles 9 on which the McMillan model is based; the Wulf model helps to explain these cases. In 1975, 10 Wulf suggested that the origin of tilt of the SmC phase depends on steric factors and packing forces. He concluded that the time-average shape of the mesogens in the SmA phase is cylindrical, which allows the molecules to rotate freely around the molecular long axis, and therefore pack vertically. In contrast, at lower temperature and after transition into the SmC phase, molecular rotation becomes more restricted around the long axis. Then, the molecules (rod-like mesogen ) adopt a time-averaged zig-zag conformation that corresponds to the lowest energy conformation for calamitic molecules in the SmC phase as shown in Figure 1-9. Figure 1-9: Schematic representation of the Wulf model. 1.3 Chirality in the Smectic C Phase Liquid crystal materials are anisotropic and exhibit birefringence, an optical property in which the plane of polarized light is rotated; this property is important for technological 8

23 applications. Current research efforts are focused more on the chiral SmC phase as a light shutter, which provides several advantages 7. These topics will be discussed in the following sections Chiral Smectic C (SmC*) Phase Ferroelectric Liquid Crystals The chiral SmC phase (denoted as SmC*) has the same structural features as the SmC phase. The SmC phase is biaxial, and the direction of translational order is characterized by the director n and layer normal z in the smectic tilt plane. The director n and layer normal z form a tilt angle θ. However, a chiral tilted smectic phase has additional properties that are not observed with achiral molecules, such as spontaneous polarization (Ps), which is present in the absence of an electric field. This electric polarization is known as a ferroelectric property of the SmC* phase. This property was first predicted by Meyer in , based on the fact that SmC has two symmetry elements: a twofold rotational axis axis perpendicular to the tilt plane (C2) and a mirror plane congruent with the tilt plane (σ) (Figure 1-10). When we move from the non-chiral SmC to the chiral SmC*, the symmetry of the phase is reduced from C2h to C2, where there is no symmetry plane. This result leads to polarization and form polar order. However, in the absence of outside constraints, the net spontaneous polarization of the bulk material is equal to zero because the Ps vector rotates from one layer to the next in the SmC* phase to form a macroscopic helical structure, as shown in Figure The helical structure is another chiral property of the the SmC* phase. In 1980, Clark and Lagerwall 12 showed that when the SmC* phase is aligned between two rubbed polyimide-coated glass slides, the helical structure unwinds to give a surface- 9

24 stabilized ferroelectric liquid crystal (SSFLC) film which exhibits a net spontaneous polarization perpendicular to the plane of the glass slides (Figure 1-11). Figure Schematic representations of symmetry elements of achiral SmC phase and SmC* phase after chiral doping. Figure Schematic representations of macroscopic helical arrangement of SmC* phase in bulk material (left) and in surface-stabilized state (right) 12. Typically, LCDs work through the application of an electric field. As a result of the birefringent properties of the LC materials, when an electric field is applied across the 10

25 SSFLC film, the LCs are switched between two opposite tilt orientations, +θ to θ, as shown in Figure 1-12, thus creating an ON/OFF light shutter between crossed polarizers. Figure Schematic representation of ON/OFF light shutter (+θ and θ directions) in SSFLC. Non-chiral liquid crystal molecules are also able to present chiral structures if doped with a chiral additive. Kuszynski and Stegemeyer showed that Ps and ferroelectric properties of the chiral SmC* phase can be exhibited by dissolving a chiral dopant in a non-chiral SmC mesogenic material 13. The design of commercial liquid crystal SmC* displays has been achieved by adding a small amount of a chiral dopant with high polarization power into an achiral, low viscosity SmC mixture 13. SmC* materials have received much attention because the switching times achieved by SSFLC light shutters are significantly faster than those of LCDs that use nematic liquid crystals. The switching time between the +θ and θ tilt orientations of a SSFLC shutter depends on the rotational viscosity (η), the applied field (E), and the Ps of the materials. 14 τ γ sin θ P s E (1.2) 11

26 1.3.2 SSFLC Display Technology Problems Although the SSFLC display has achieved success, it does have some drawbacks. The major problem with the application of SSFLCs is that the smectic layers usually shrink by ~7-10% during the transition from the non-tilted SmA* phase to the tilted SmC* phase when aligned between the two glass slides of the display system. As a result, a chevron geometry is formed and it is difficult to achieve the bookshelf configuration (Figure 1-12) in which the smectic layers are nearly parallel to the glass substrates 2. When a SmA* phase is confined between the glass substrates of a display device, it exists in the bookshelf configuration. Upon cooling from the SmA* to the SmC* phase in the glass cell, the smectic layers contract, but the molecules are still anchored at the glass surfaces by the rubbed polymer substrate 2. This results in the formation of chevron-shaped layers, folding in opposite directions with zigzag defects, as shown in Figure 1-13 b. Figure (a) The SmA* phase in the bookshelf configuration. (b) the SmC*phase in the chevron configuration 2. In 1987, 15 Rieker and coworkers were able to experimentally confirm the presence of these chevron defects. When the chevron structures are arranged in opposite directions, they 12

27 create free volume that results in the aforementioned zigzag defects, as shown in Figure The zigzag defects degrade the quality of an FLC device, leading to image irregularities. Figure A picture of zigzag defects in a SmC* phase de Vries-like Materials The problem of chevron formation and zigzag defects during the SmA SmC transition in SSFLC devices has stimulated a great deal of research, and materials with unusually small layer contractions of less than 1% have been discovered. These materials are called de Vrieslike. 16,17 To explain why these molecules tilt with a small layer contraction in the SmA SmC transition, two approaches have been considered: the diffuse cone model and the combination of low orientational order and high lamellar order De Vries Diffuse Cone Model Initially based on the classic rigid rod model shown in Figure 1-15a, the SmA phase director n is oriented along the smectic layer normal z. Upon cooling from the SmA to the SmC 13

28 phase, the molecules are tilted from z by the tilt angle θ. The layer spacing of the SmC phase (dc) is related to the layer spacing of the SmA phase (da) by the cosine of the tilt angle θ, as given by Equation (1.3). The layer contraction between the SmA and SmC phases, (da dc)/da, in terms of the tilt angle θ, is given by Equation (1.4). d C = d A cos θ (1.3) (d A d C ) d A = 1 cos θ (1.4) Figure Schematic representation of the (a) rigid rod model and (b) diffuse cone model 17. The behavior of the new de Vries-like materials has been explained in a different approach via the diffuse cone model, proposed by de Vries in According to this model, the molecules in the SmA phase adopt a lamellar structure in which the molecular axes are tilted away from the director n, but with random azimuthal directions. Thus, there is no significant change in molecular tilt in the transition between the SmA and SmC phases, which 14

29 has been described as azimuthal ordering, as shown in Figure 1-15b. As a result, the de Vrieslike materials have unusually small layer contractions. The de Vries-like character of a material can be measured by a reduction factor R, according to Equation (1.5). R is the ratio of the smectic tilt angle (T) that is required to give a layer contraction d/dac(t) at a temperature T below the transfer point TAC from the SmA to the SmC phase, over the optical tilt angle (θopt) measured by polarized optical microscopy (POM). 18 R = δ(t)/θ opt (T) = cos 1 (d C (T))/d(T AC ) /θ opt (T) (1.5) Low Orientational Order and High Lamellar Order More recently, studies by the Lemieux group 19 suggested that materials require a low orientational order parameter S2 in order to achieve de Vries-like behavior. The majority of de Vries-like liquid crystals have S2 values in the range of , whereas these values in conventional liquid crystal SmA and SmC phases are typically ~ In addition, de Vries-like behavior has been observed for smectic layers with high lamellar order which are stabilized by nanosegregating end groups Nanosegregation Usually, nanosegregation occurs with amphiphilic molecules, which have both hydrophilic and hydrophobic parts. The incompatible parts of these molecules tend to segregate 15

30 into distinct nanoscale domains 5. Nanosegregation among the cores and alkyl chains in rodshaped mesogens effectively promotes the formation of smectic layers, and end groups such as organosiloxanes and carbosilanes have been shown to promote lamellar ordering 2,21, the formation of smectic phases, and a suppression of the nematic phase. As a result of the tendency of organosiloxanes and carbosilanes, as well as hydrocarbon groups, to nanosegregate into sublayer spaces, intercalated smectic bilayers inside a lamellar structure are formed, as shown in Figure (1-16) 20,23. The figure shows that there are three incompatible segments the aromatic core, the alkyl chain, and the siloxane group which give rise to the nanosegregated bilayer structure. Figure Organization of the oligosiloxane-containing liquid crystals in the smectic Layer (ref. 22). 16

31 Mesogenic materials that contain organosilicon groups are characterized by the stability of their SmC phases, which may be due to the formation of virtual siloxane backbones by the mesogens, because of the nanosegregation that decreases the entropic expense of the molecular tilt Examples of Known Carbosilane-Terminated de Vries-like Materials Recently, researchers have used chemically inert carbosilane end groups instead of hydrolytically labile organosiloxane end groups because the former are better suited for liquid crystal displays 20. In recent years, the Lemieux group has developed a new design for liquid crystal mesogens which is based on the combination of a SmC-promoting element and a SmApromoting element 20,23. There are two examples for this design. The first is the mesogen QL6-6 23, which has a carbosilane end group that promotes the SmC phase by virtue of nanosegregation, as well as a chloro-terminated alkyl SmA-promoting element. Second, the mesogen QL also has a carbosilane end group that promotes the SmC phase, in addition to a 5-phenylpyrimidine core as the SmA-promoting element. Both materials undergo a SmA SmC transition with a layer contraction of %. The reduction factor R values for these mesogens are 0.20 and 0.17, respectively 19,23,24. 17

32 1.5.1 The Effect of Carbosilane Nanosegregation on de Vries-like Properties To investigate the connection between de Vries-like properties and the length of the carbosilane end-group, a homologous series of carbosilanes was synthesized in a recent study by Lemieux group: the tricarbosilane QL13-n, dicarbosilane QL18-n, and monocarbosilane QL19-n 19. Small angle X-ray scattering (SAXS) data revealed that the de Vries-like behavior depends on the length of the nanosegregating carbosilane end group, and increases from the monocarbosilane to the tricarbosilane. Nanosegregation was the key to observing any de Vries-like behavior in these materials. In addition, the results showed that the nanosegregating carbosilane end groups created high lamellar ordering, which was also required to achieve de Vries-like behavior. The shortening of the carbosilane length reduced the lamellar ordering of the mesogens, which was indicated by the reduction factor R and the change in layer spacing (Figure 1-17). The reduction factor R increased with the decrease in the length of the nanosegregating carbosilane end groups in these mesogens. 18

33 Figure Smectic layer spacing d/dac versus the reduced temperature T TAC for mesogens QL13-3, QL18-3, QL19-6, and QL28-6/6 (from ref. 19). From 2D X-ray scattering analyses of monodomains, the orientational order (S2) was found to be influenced by the length of the carbosilane end group: S2 decreases with increasing length of the carbosilane end group, as shown in Figure There is a small change in S2 between QL28-6/6 and QL19-6, but S2 decreases significantly between QL19-6 and QL18-3 or QL13-3, as shown in Table 1-1. The low orientational order that is also required to achieve de Vries-like behavior in these materials supports the hypothesis that increasing de Vrieslike behavior requires high lamellar order and low orientational order. However, we still do not understand why orientational order decreases with increasing length of the carbosilane endgroup. 19

34 Figure Orientational order parameter (S2) versus reduced temperature T TAC for mesogens QL13-3, QL18-3, QL19-6, and QL28-6/6 (from ref. 19). Table 1-1. Liquid crystal layer dac spacings, orientational order parameter S2 and reduction factor R at T TAC = 10 K. Compound dac / Å S 2 R QL QL QL QL28-6/ Hypothesis From previous study of the effect of carbosilane nanosegregation on de Vries-like properties, one can assume that the tricarbosilane end-group is approximately spherical in shape as a result of shallow torsional energy profiles. Therefore, in the intercalated bilayer structure formed by carbosilane-terminated mesogens, nanosegregation may produce a significant amount of free volume in the hydrocarbon sub-layer, which would be backfilled 20

35 by an increase in orientational fluctuations to minimize the free energy. The requirement for such orientational fluctuations would be decreased for the mono- and dicarbosilane end groups due to their smaller steric bulks compared to the tricarbosilane, as depicted in Figure This is consistent with the orientational order parameter S2 being inversely proportional to the length of the carbosilane end group (see Table 1-1). Figure Schematic representations the bulky size of the monocarbosilane end-group (left) and tricarbosilane (right) Test of Hypothesis To test this hypothesis, we have investigated the effects of reducing the free volume in the intercalated bilayers of a series of tricarbosilane dimers (QL40-n) by comparing their properties to those of the corresponding monomers (QL39-n), including measurements of S2. We assume that the dimers with the tricarbosilane spacer will form intercalated bilayers similar to those shown in Figure However, in this case, the spacer will be forced into more extended conformations by the lamellar ordering of the two mesogenic units extending 21

36 in opposite directions along the layer normal z, which should result in a smaller time-average cross-section Project Outline The purpose of this project is to test the hypothesis and investigate the mesogenic properties of the model tricarbosilane dimers QL40-n using the 2-PhP mesogenic scaffold, for comparison with the mesogenic monomers QL39-n, with the ultimate objective of understanding the origin of de Vries-like behavior in carbosilane-terminated mesogens. This thesis describes the synthesis of the liquid crystals and their characterization by polarized microscopy, DSC measurements and X-ray scattering experiments. QL39-n, n=5-10 QL40-n, n=

37 1.7 References (1) Reinitzer, F. Monatsh. Chem.1888, 9, 421. (2) Lagerwall, J. P. F.; Giesselmann, F. ChemPhysChem 2006, 7, (3) Demus, D.; Goodby, J.; Gray, G. W.; Spiess, H. W.; Vill, V. Handbook of Liquid Crystals, Volume 7: Liquid Crystal Dimers and Oligomers, (4) Imrie, C. T. Liquid Crystals II, Volume 95: Liquid Crystal Dimers, (5) Tschierske, C. J. Mater. Chem. 1998, 8, (6) Vizitiu, D.; Lazar, C.; Halden, B.; Lemieux, R. J. Am. Chem. Soc. 1999, 121(36), (7) Demus, D.; Goodby, J.; Gray, G. W.; Spiess, H. W.; Vill, V. Handbook of Liquid Crystals, Volume 2A: Low Molecular Weight Liquid Crystals I, (8) McMillan, W. L. Phys. Rev. A 1973, 8, (9) Goodby, J. W.; Gray, G. W.; McDonnell, D. G. Mol. Cryst. Liq. Cryst. 1977, 34, 183. (10) Wulf, A. Phys. Rev. A 1975, 11, 365. (11) Meyer, R. B.; Liebert, L.; Strzelecki, L.; Keller, P. J. Phys. (Paris), Lett. 1975, 36, L69- L71. (12) Clark, N. A.; Lagerwall, S. T. Appl. Phys. Lett. 1980, 36, 899. (13) Kuczynski, W.; Stegemeyer, H. Chem. Phys. Lett. 1980, 70, (14) Handschy, M. A.; Clark, N. A.; Appl. Phys. Lett. 1982, 41, 39. (15) Rieker, T. P.; Clark, N. A.; Smith, G. S.; Parmer, D. S.; Sirota, E. B.; Safinya, C. R. Phys. Rev. Lett. 1987, 59,

38 (16) De Vries, A. Mol. Cryst. Liq. Cryst. 1977, 41, (17) De Vries, A. J. Chem. Phys. 1979, 70, (18) Radcliffe, M. D.; Brostrom, M. L.; Epstein, K. A.; Rappaport, A. G.; Thomas, B. N.; Shao, R.; Clark, N. A. Liq. Cryst. 1999, 26, (19) Mulligan, K. M.; Bogner, A.; Song, Q.; Shubert, P. J.; Giesselmann, F.; Lemieux, R. P. J. Mater. Chem. C 2014, 2, (20) Song, Q.; Nonnenmacher, D.; Giesselmann, F.; Lemieux, R. P. J. Mater. Chem. C 2013, 1, 343. (21) Shoosmith, D.; Carboni, C.; Perkins, S.; Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A. 1999, 331, (22) Ibn-Elhaj, M.; Skoulios, A.; Guillon, D.; Newton, J.; Hodge, P.; Coles, H. J. Liq. Cryst. 1995, 19, 373. (23) Song, Q., Bogner, A., Giesselmann, F., & Lemieux, R. P. Chem. Commun. 2013, 49, (24) Schubert, C. P.; Bogner, A.; Porada, J. H.; Ayub, K.; Andrea, T.; Giesselmann, F.; Lemieux, R. P. J. Mater. Chem. C 2014, 2, (25) Robinson, W. K.; Carboni, C.; Kloess, P.; Perkins, S. P.; Coles, H. J. Liq. Cryst., 1998, 25, 301. (26) Lemieux, R. P. 24

39 Chapter 2. 2-Phenylpyrimidine Monomeric and Dimeric Tricarbosilane Liquid Crystals 2.1 Syntheses The synthesis of the monomeric series QL39-n was carried out by selective alkylation of 2-(4-hydroxyphenyl)pyrimidin-5-ol (1), which is commercially available, with the appropriate alcohols via Mitsunobu reactions to give 2-n (Scheme 2-1). A second alkylation with 1-bromo-12,12,14,14,16,16-hexamethyl-12,14,16-trisilaheptadecane gave QL39-n in 80-95% yield. Alternatively, alkylation of 2-n with 10-undecen-1-ol via a Mitsunobu reaction gave 3-n, which was converted to QL39-n via a platinum-catalyzed hydrosilation reaction using 1,1,1,3,3,5,5-heptamethyltrisilane and Karstedt s catalyst. The synthesis of the dimeric series QL40-n was carried out by alkylation of 2-n with 1,27-dibromo-12,12,14,14,16,16- hexamethyl-12,14,16-trisilaheptacosane in 42-60% yield, as shown in Scheme 2-1. The monomers and dimers compounds were recrystallized from ethanol. Scheme 2-1 Reagent and conditions: (a) CnH2n+1OH, DIAD,PPh3,THF, rt, overnight or CnH2n+1Br K2CO3, methyl ethyl ketone, reflux, overnight; (b) C11H21OH, DIAD, PPh3, THF, rt.overnight; (c) 1,1,1,3,3,5,5-heptamethyltrisilane, Karstedt s catalyst, toluene, 48 h; (d) 1- bromo-12,12,14,14,16,16-hexamethyl-12,14,16-trisilaheptadecane, K2CO3, methyl ethyl ketone. 25

40 Scheme 2-2 Reagent and conditions: (a) K2CO3, methyl ethyl ketone, reflux, overnight. 2.2 Mesophase Characterization The mesophases formed by the QL39-n monomers and QL40-n dimers were characterized using polarized optical microscopy (POM) in Figure 2-1, 2-2 and differential scanning calorimetry (DSC) in Figure 2-3, 2-4. All the QL39-n monomeric mesogens in the series n = 5 10 exhibited only a low-birefringence grey Schlieren texture upon heating and cooling, which is characteristic of the SmC phase (Figure 2-1). On the other hand, the QL40- n dimers formed a SmA phase on cooling from isotropic liquid, as shown by the characteristic fan textures and dark homeotropic domains (Figure 2-2a). We also observed significant changes in texture at lower temperatures below the SmA phase for QL40-5, QL40-6, QL40-7, and QL40-8, where the dark homeotropic domains transformed to a grey texture. This implies that the phase was tilted, however, no broken fans were observed (Figure 2-2b). Furthermore, this change was accompanied by a change in interference colors, which generally results from a change in the birefringence. Hence, this unidentified phase was denoted as a SmX phase. This change, which was not detected via DSC (Figure 2-4) and for which it was impossible to measure the optical tilt angles (θopt) using POM, may be due to an unusual layer contraction of the dimer structure. We will see later, through the results of X-ray scattering 26

41 experiments and electro-optic response analysis, that this phase does not behave like either the SmC phase, or the SmCa (anticlinic) phase, in which the molecules of two adjacent layers have opposite tilt orientations. Furthermore, the fact that the SmA phase is not observed for the monomeric series suggests that the properties of the dimer and monomer are clearly different. Figure 2-1: Polarized photomicrograph of QL39-6 monomer on cooling: SmC phase at 70 C. (a) (b) Figure 2-2: Polarized photomicrographs of QL40-6 dimer on cooling: (a) SmA phase at 91 C and (b) SmX phase at 74 C. 27

42 Figure 2-3: DSC profile for QL39-6 compound taken at 5 K/min scan rate. Figure 2-4: DSC profile for QL40-6 compound taken at 5 K/min scan rate. 28

43 T C Figure 2-5: Phase transition temperatures C for QL39-n monomeric series and QL40-n dimeric series measured via DSC upon heating at 5 K/min rate. As shown in Figure 2-5, the temperature ranges of the SmC and SmA phases formed by the QL39-n and QL40-n series, respectively, tend to have similar ranges for C6 C8, narrower with C5, and broader with C10. In addition, the SmX range in QL is similar on average at approximately 21 K. In general, going from the monomer to dimer causes a significant increase in the clearing point (by 27 K on average), which corresponds to an increase in the stability of the smectic layer 1 (the smectic mesophase exists on dimers and monomers at temperatures above room temperature). The difference in the observed clearing points may reflect a difference in the degree of nanosegregation on the momomer and dimer. Furthermore, the dimers QL40-n exhibit a more significant increase in their melting points (by 30 K on 29

44 average) relative to the corresponding monomers, except in the case of the C9 and C10 dimers, for which the melting points decrease by 24 and 20 K, respectively (Figure 2-5). In both series, the enthalpy changes are consistent with first-order transitions from the crystalline-smectic and smectic-isotropic liquid transitions. The transition temperatures and enthalpies of transition measured via DSC for the monomers and dimers are listed in Table 2-1. Table 2-1 Transition temperatures C and enthalpies of transition (kj mol -1, in parentheses) for QL39- n and QL40- n compounds. Compounds Cr SmX SmA SmC I QL (40) 57 (7) QL (43) 69 (9) QL (49) 71 (8) QL (43) 77 (10) QL (59) 77 (8) QL ( 41) 84 (11) QL (79) (11) QL (72) (15) QL (74) (16) QL (66) (14) QL (46) 96 (12) QL (40) 100 (19) 30

45 2.3 X-ray Scattering Experiments In order to investigate the structure of the smectic phases formed by the dimeric mesogens, small-angle X-ray scattering (SAXS) and monodomain 2D X-ray scattering were performed. The layer spacing d was measured as a function of temperature for the QL40-6 dimer using SAXS in accordance with Bragg s equation: nλ = 2dsinθ (2.1) where n is a positive integer and is the wavelength of the incident radiation. As shown in Figure 2-6, d was measured upon heating from the crystalline phase, and it is more or less invariant of temperature between 84 and 102 C. It decreased significantly at lower temperatures, with a maximum layer contraction of 9 %. Furthermore, the apparent transition point is identical to that for the SmA-SmX phase transition, for which the dark homeotropic domains transition to a grey texture under POM; this would appear to be consistent with a conventional SmA-SmC transition. The d values obtained from X-ray analysis of the SmA phase (42.5 Å) are smaller than the length of the fully extended QL40-6 (L= 73.3 Å), calculated according to the model (Figure 2-7). The ratio of d/l = 0.57 suggests that the molecules in the SmA phase have a intercalated bilayer arrangement 2. This arrangement is a typical result of mixing between a terminal chain and spacer in a dimer 2,3. In addition, the stability of this arrangement depend on the nature of the interaction between the spacer (tricarbosilane) and the end alkyl chains 2. The 2D X-ray scattering patterns for QL-40-6 at T TAX = +15 K and T TAX = -10 K are shown in Figure 2-8. Both patterns show the known features of the X-ray diffraction (XRD) patterns of the SmA phase at both 70 and 100 C. The X-ray patterns exhibit layered structure 31

46 characteristics that are observed as a sharp Bragg reflection along the layer normal z in the small-angle region; these characteristics correspond to smectic layering. In addition, a diffuse wide-angle scattering is observed along the axis orthogonal to z, which corresponds to the intermolecular distances of the hydrocarbon and carbosilane segments 4. This analysis via 2D X-ray scattering of a monodomain shows no azimuthal rotation of the wide-angle reflection relative to the small-angle reflection at the apparent SmA-SmX transition point (Figures 2-8). This is clearly shown in Figure 2-9 in which both small and wide angle intensity profiles versus azimuthal angle at 70 C are compared. This is inconsistent with the observation of behavior such as transformation of the dark homeotropic domains to a grey texture, which, at first, suggests a SmC phase organization. Figure 2-6. Smectic layer spacing d versus reduced temperature T Tx for QL40-6 compound. Figure 2-7. Fully extended calculated model of QL40-6 dimer at 3D Optimization (ACDLABS/3D). 32

47 Figure D X-ray scattering patterns at T TAX = +15 K and T TAX = -10 K (left), and diffuse wide-angle scattering as function of azimuthal angle for QL40-6 at 70, 85 and 100 C (right). Figure 2-9. χ scan for the wide-angle and small-angle at

48 To understand the behavior of the QL40-6 dimer more fully, we measured the orientational order parameter S2 from 2-D X-ray scattering measurements of the wide-angle azimuthal intensity profiles I(χ), which are obtained by integrating the intensity results from the 2D X-ray diffraction patterns. As shown in Figure 2-10, the phase transition from SmA to SmX is not discernible in the S2 profile; that is, no clear jump is apparent, and it is therefore difficult to assume that the interference color change observed in the texture analysis (the color changed from red to green during the SmA to SmX transition, as shown in Figure 2-2) is consistent with a change in the S2 values. Figure Orientational order parameter S2 vs. temperature for QL40-6 compound Electro-Optic Response In order to confirm that the QL40-6 dimer does not form a tilted smectic phase or an anticlinic phase, we investigated the electro-optical behavior of the mesophases formed by the monomer QL39-6 and QL40-6 upon doping with the chiral dopant QL32-6 (5 mol%) 5, using POM. The two samples were introduced in commercial indium-tin oxide (ITO) glass slides with a rubbed nylon alignment substrate (4.0-µm spacing). The doped QL39-6 sample, which forms a SmC* phase only, exhibited good alignment, with contrasting dark and bright texture domains. 34

49 Furthermore, application of a triangular wave voltage across the film (6 V/µm, 100 Hz) produced a polarization reversal current response consisting of one polarization peak, which is consistent with a ferroelectric ground state that is consistent with a SmC* phase (Figure 2-11 a). On the other hand, the doped QL40-6 sample, which was aligned under the same conditions, did not respond to a triangular wave voltage across the film for either the high-temperature SmA* and low-temperature SmX*. This sample did not exhibit any polarization reversal current or any evidence of switching behavior under POM (Figure 2-11b). Hence, both the electro-optical response behavior and the results of the X-ray measurements confirm that the SmX mesophase formed by the QL40-6 dimer is neither a synclinic SmC phase nor an anticlinic SmCa. Note that the latter would exhibit antiferroelectric behavior upon doping with QL32-6, which would show two polarization reversal current peaks instead of one, as shown in Figure QL32-6 (a) (b) Figure Polarization reversal current profiles for surface-stabilized films (4 µm) of (a) QL39-6 and (b) QL40-6 (in the SmX phase), both doped with the chiral mesogen QL32-6 (5 mol%), upon application of triangular AC voltage of 6 V/µm and 100 Hz. 35

50 Figure Two polarization current peaks appear for smectic C antiferroelectric phase in response to triangular voltage waveform (ref. 6). 2.5 SmX phase The SmX phase formed by the dimer exhibits unusual and complex behavior that is clearly different from that observed for the corresponding monomer. The SmA phase formed by QL40-6 (identified via POM) was confirmed by XRD. Further, the SmX phase in the same compound appears to be a SmA phase with an unusual layer contraction. In order to understand the behavior during the change from monomer to dimer, we must obtain a structural model for QL40-6. It is important to note that the monomeric molecules are essentially different from the dimeric molecule with respect to the molecular length and the density of the molecular endgroups. From Mulligan 7, we understand the monomer in which the carbosilane end-groups are accommodated in the layers,and also how the compound having a bilayer intercalated arrangement with nanosegregation produces a significant amount of free volume in the hydrocarbon sub-layer. QL40-6 also forms a bilayer intercalated arrangement that retains a constant d value corresponding to half the molecular length. 36

51 Ultimately, the difference between the two models is that the one incorporating the tricarbosilane spacer will not have a spherically shape on the time average like that predicted for the tricarbosilane end-group. This is because the molecules are oriented perpendicular to the layers, with the two mesogenic units extending in opposite directions along z (system uniaxiality) 6, which will result in a tricarbosilane spacer with more extended conformations (Figure 2-13). Therefore, a tricarbosilane spacer should have a smaller cross-section on the time-average. We note that a monocarbosilane end-group with a small cross-section has a lower degree of nanosegregation a tricarbosilane end-group, which reduces the degree of SmCpromotion character of the carbosilane unit and may explain why QL40-n forms an SmA phase instead of an SmC phase. In the case of the SmX phase, d contracts with decreasing temperature, which may be a consequence of an increase in core-core interactions that drives an increase in intercalation. Figure Schematic representation of bulky size of tricarbosilane unit for dimer SmA phase. 37

52 2.7 Conclusions The two new series of carbosilane liquid-crystal dimers and monomers were synthesized with a 2-phenylpyrimidine scaffold and tricarbosilane spacer and end-groups, respectively. The results clearly show that the dimers and monomers have very different mesomorphic properties, which may be related to the difference in flexibility of the tricarbosilane units in a lamellar organization. The monomers (QL39-n) form only a tilted SmC phase, whereas the dimers QL40-n form an orthogonal SmA phase together with a lower temperature SmX phase. The SmX phase has shown some characteristics of the SmC phase, including a birefringent Schlieren texture and a contraction of the layer spacing, but 2- dimensional X-ray scattering and electro-optical response experiments strongly suggest that the SmX is an orthogonal phase with unusual layer contraction of the dimer structure. Furthermore, the observed increase in clearing point from the monomers to dimers may reflect a difference in the degree of nanosegregation on the monomers and dimers as well as a difference in the strength of van der Waals interactions between the core structures. This would be consistent with our hypothesis that the tricarbosilane spacer in QL40-n has a smaller crosssection on the time- average compared with the monomer 7. It remains unclear why the layer spacing in QL40-n decreases upon SmA-SmX transition, although one might speculate that the layer contraction is due to an increase in the degree of interdigitation. 38

53 2.7 Reference (1) Dunmur, D. Liquid Crystal Fandmantals; Physical Properties of Liquid Crystal, 2002 (2) Demus, D.; Goodby, J.; Gray, G. W.; Spiess, H. W.; Vill, V. Handbook of Liquid Crystals, Volume 7: Liquid Crystal Dimers and Oligomers, (3) Imrie, C. T.; Henderson, P. A. Chem. Soc. Rev., 2007, 36, (4) Schubert, C. P.; Bogner, A.; Porada, J. H.; Ayub, K.; Andrea, T.; Giesselmann, F.; Lemieux, R. P. J. Mater. Chem. C 2014, 2, (5) Schubert, C. P.; Müller, C.; Wand, M. D.; Giesselmann, F.; Lemieux, R. P. Chem. Commun., 2015, 51. (6) Robinson, W. K.; Carboni, C.; Kloess, P.; Perkins, S. P.; Coles, H. J. Liq. Cryst., 1998, 25, 301. (7) Mulligan, K. M.; Bogner, A.; Song, Q.; Shubert, P. J.; Giesselmann, F.; Lemieux, R. P. J. Mater. Chem. C 2014, 2,

54 Chapter 3. Experimental 3.1. Syntheses and Characterization General 1 H NMR and 13 C NMR spectra were recorded using a Bruker Avance 400 spectrometer; chemical shifts are reported in parts per million (ppm) relative to tetramethylsilane (TMS). Mass spectra were recorded using using a Waters/Micromass GC-TOF ( low resolution and high resolution) in electron impact ionization (EI) mode. Differential scanning calorimetry (DSC) analyses were performed on a TA Instruments Q2000 instrument with scanning rate of 5 K min -1. Texture analyses were performed using a Nikon Eclipse E600 POL polarized microscope fitted with a Linkam LTS 350 hot stage and TMS 93 temperature controller. Smallangle X-ray scattering experiments were performed on a SAXSess system from Anton Paar GmbH. Unaligned samples (filled into Hilgenberg Mark capillary tubes of 0.7 mm diameter) were mounted in a temperature controlled sample holder unit (TSC 123). The X-ray beam from a ceramic 107 tube generator was focused by a bent multilayer mirror and shaped by a line collimation block. The X-ray scattering was recorded with a CCD detector (KAF 2084x2083 SCX) and processed and analysed using the SAXSquant 3.5 software Materials All solvents and reagents were obtained from commercial source and used without further purification unless otherwise noted. Anhydrous THF and toluene were obtained from a Solv- 40

55 Tek, Inc. solvent purification system. Chemical were obtained from commercial source except for 2,2,4,4,6-pentamethyl-2,4,6-trisilaheptane, which was synthesized by Dr. Kirk Mulligan according to literature procedures 1, and 1,27-dibromo-12,12,14,14,16,16-hexamethyl-12,14,16-trisilaheptacosane, which was synthesized by Dr. Christopher Schubert Synthesis of QL39-n Liquid Crystal Monomers Reagent and conditions: (a) CnH2n+1OH, DIAD,PPh3,THF, rt, overnight or CnH2n+1Br K2CO3, methyl ethyl ketone, reflux, overnight; (b) C11H21OH, DIAD, PPh3, THF, rt.overnight; (c) 1,1,1,3,3,5,5-heptamethyltrisilane, Karstedt s catalyst, toluene, 48 h; (d) 1-bromo- 12,12,14,14,16,16-hexamethyl-12,14,16-trisilaheptadecane, K2CO3, methyl ethyl ketone. 4-(5-Pentyloxypyrimidin-2-yl)phenol (2-5). To a mixture of 2-(4-hydroxyphenyl)pyrimidin -5-ol (1, 2.0 g, 10.6 mmol), pentan-1-ol (9.34 g, 10.6 mmol) and Triphenylphosphine (PPh3) (5.24 g, 20.2 mmol) in dry Tetrahydrofuran (THF) (100 ml) was added dropwise Diisopropyl azodicarboxylate (DIAD) (4.04 g, 20.2 mmol) at room temperature. After stirring for 24 h, the solvent was removed under reduced pressure and the solid residue was purified by column chromatography on silica gel (3:1 hexane/etoac) to give 2-5 as a beige solid (1.5 g, 55%): 1 H NMR (400 MHz, CDCl3) δ (ppm) 8.44 (s, 2 H), 8.27 (d, J = 9.1 Hz, 2 H), 6.95 (d, J = 8.8 Hz, 2 H), 5.15 (s, 1 H), 4.09 (t, J = 6.4 Hz, 2 H), 1.84 (m, 2 H), (m, 4 H), 0.96 (t, J = 6.6 Hz, 3 H): 13 C NMR (100 MHz, CDCl 3) δ 160.1, 157.7, 151.2, 143.9, 131.3, 129.4, 115.6, 69.1, 41

56 28.7, 28.0, 22.4, 14.0; LRMS (EI) m/z 258 ([M] +,48), 189 (17), 188 (100),159 (12), 132 (20), 119 (34), 105 (18) ; HRMS (EI) m/z calcd for C 15H 18N 2O , found (5-Hexyloxypyrimidin-2-yl)phenol (2-6). The procedure described for the synthesis of 2-5 was repeated with hexan-1-ol (1.08 g, 10.6 mmol) and 2-(4-hydroxyphenyl)pyrimidin -5-ol (2.0 g, 10.6 mmol) to give 2-6 as a beige solid (1.46 g, 50%): 1 H NMR (400 MHz, CDCl3) δ (ppm) 8.43 (s, 2 H), 8.20 (d, J = 9.1 Hz, 2 H), 6.83 (d, J = 8.8 Hz, 2 H), 5.21 (s, 1 H), 4.09 (t, J = 6.4 Hz, 2 H), (m, 2 H), (m, 2 H), 1.36 (dq, J = 7.2, 3.6 Hz, 4 H), 0.98 (t, J = 6.6 Hz, 3 H): 13 C NMR (100 MHz, CDCl3) δ 160.1, 157.5, 151.2, 143.9, 130.0, 129.3, 115.5, 69.0, 31.5, 29.0, 25.5, 22.4, LRMS (EI) m/z 272 (M+, 55), 189 (14), 188 (100), 159 (6), 132 (8), 105 (4); HRMS (EI) m/z calcd for C16H20N2O , found (5-Heptyloxypyrimidin-2-yl)phenol (2-7). The procedure described for the synthesis of 2-5 was repeated with heptan-1-ol (1.23 g, 10.6 mmol) and 2-(4-hydroxyphenyl)pyrimidin -5-ol (2.0 g, 10.6 mmol) to give 2-7 as a beige solid (1.8 g, 59%): 1 H NMR (400 MHz, CDCl3) δ (ppm) 8.42 (s, 2 H), 8.25 (d, J = 8.8 Hz, 2 H), 6.92 (d, J = 8.8 Hz, 2 H), 4.97 (s, 1 H), 4.09 (t, J = 6.4 Hz, 2 H), (m, 2 H), (m, 2 H), (m, 6 H), 0.91 (t, J = 6.9 Hz, 3 H): 13 C NMR (100 MHz, CDCl3) δ 169.1, 157.5, 152.0, 143.5, 132.4, 129.1, 115.8, 68.0, 32.5, 29.3, 28.95, 25.5, 23.6, LRMS (EI) m/z 286 (M+, 90), 202 (38), 189 (32), 188 (100), 159 (5), 57 (21); HRMS (EI) m/z calcd for C17H22N2O , found (5- Octyloxypyrimidin-2-yl)phenol (2-8). The procedure described for the synthesis of 2-5 was repeated with octan-1-ol (1.30 g, 10.6 mmol) and 2-(4-hydroxyphenyl)pyrimidin -5-ol (2.0 g, 10.6 mmol) to give 2-8 as a beige solid (1.40 g, 46%): 1 H NMR (400 MHz, CDCl3) δ (ppm) 8.43 (s, 2 H), 8.91 (d, J = 8.8 Hz, 2 H), 6.97 (d, J = 8.8 Hz, 2 H), 5.45 (s, 1 H), 4.09 (t, J = 6.4 Hz, 2 H), (m, 2 H), (m, 2 H), (m, 6 H), 0.92 (t, J = 6.6 Hz, 3 H): 13 C NMR (100 MHz, CDCl3) δ 160.1, 157.0, 151.0, 143.5, 131.3, 129.0, 115.2, 68.7, 31.5, 28.94, 28.85, 28.77, 25.5, 22.5, LRMS (EI) m/z 300 (M+, 44), 189 (14), 188 (100),

57 (5), 132 (6), 119 (11), 105 (50); HRMS (EI) m/z calcd for C18H24N2O , found (5- Nonyloxypyrimidin-2-yl)phenol (2-9). A mixture of 2-(4-hydroxyphenyl)pyrimidin-5- ol (2.0 g, 10.6 mmol), K2CO3 (4.39 g, 31.8 mmol) and 1-bromononane (2.20 g, 10.6 mmol) in acetone (80 ml) was heated to reflux for 24 h. After cooling, the solvent was removed under reduced pressure, and the solid residue was dissolved in DCM (60 ml) and washed with dilute HCl (1 M, 20 ml), brine (60 ml), dried (MgSO4) and concentrated. The crude product was purified by flash chromatography on silica gel (3:1 hexane/etoac) to give 2-9 as a beige solid (1.65 g, 50%): 1 H NMR (400 MHz, CDCl3) δ (ppm) 8.42 (s, 2 H), 8.91 (d, J = 8.8, 2 H), 6.97 (d, J = 8.8 Hz, 2 H), 4.94 (s, 1 H), 4.09 (t, J = 6.4 Hz, 2 H), (m, 2 H), (m, 2 H), (m, 8 H), 0.92 (t, J = 6.8 Hz, 3 H): 13 C NMR (100 MHz, CDCl3) δ 160.1, 157.3, 153.8, 144.1, 136.0, , 115.7, 68.8, 31.5, 29.7, 29.6, 29.2, 28.9, 25.9, 22.5, 14.4; LRMS (EI) m/z 314 (M+, 100), 189 (8), 188 (62), 57 (1); HRMS (EI) m/z calcd for C19H26N2O , found (5- Decyloxypyrimidin-2-yl)phenol (2-10). The procedure described for the synthesis of 2-9 was repeated with 1-bromodecane (2.35 g, 10.6 mmol) and 2-(4-hydroxyphenyl) pyrimidin - 5-ol (2.0 g, 10.6 mmol) to give 2-10 as a beige solid (1.8 g, 51%): 1 H NMR (400 MHz, CDCl3) δ (ppm) 8.42 (s, 2 H), 8.91 (d, J = 8.8 Hz, 2 H), 6.97 (d, J = 8.8 Hz, 2 H), 4.94 (s, 1 H), 4.98 (t, J = 6.4 Hz, 2 H), (m, 2 H), (m, 2 H), (m, 10 H), 0.92 (t, J = 6.8 Hz, 3 H): 13 C NMR (100 MHz, CDCl3) δ 160.8, 158.3, 152.9, 143.8, 137.0, , 115.3, 68.9, 31.8, 30.50, 29.72, 29.60, 28.96, 28.95, 25.8, 22.6, LRMS (EI) m/z 328 (M+, 100), 189 (10), 188 (85), 57 (2); HRMS (EI) m/z calcd for C20H28N2O , found Hexyloxy-2-(4-(undec-10-enyloxy)phenyl)pyrimidine (3-6). The procedure described for the synthesis of 2-5 was repeated with 2-6 (1.46 g, 5.3 mmol) and 10-undecen-1-ol (0.90 g, 43

58 5.3 mmol), to give 3-6 as a yellow solid (0.93 g, 41%): 1 H NMR (400 MHz, CDCl3) δ (ppm) 8.42 (s, 2 H), 8.28 (d, J = 8.84 Hz, 2 H), 6.98 (d, J = 8.84 Hz, 2 H), 5.82 (ddt, J = 17.05, 10.29, 6.66, 6.66 Hz, 1 H), (dd, 2 H), (two separate triplets m, 4 H), 2.05 (q, J = 6.82 Hz, 2 H), (m, 4 H), (m, 18 H), (t, 3 H). 13 C NMR (100 MHz, CDCl3) δ 157.6, 151.0, 143.3, 139.2, 130.0, 128.9, , , 68.94, 68.06, 33.7, 31.49, 29.50, (several overlapping peaks), 28.9, 26.0,25.5, 22.5, 14.0 LRMS (EI) m/z 424 ([M] +, 17), 303 (4), 272(15), 188 (100),107 (4), 81 (13), 67(18) ; HRMS (EI) m/z calcd for C27H40N2O , found Pentyloxy-2-[4-(12,12,14,14,16,16-hexamethyl-12,14,16-trisilaheptadecyloxy)phenyl] pyrimidine (QL39-5). A mixture of 2-5 (0.23 g, mmol), K2CO3 (0.85 g, 6.16 mmol) and 1-bromo-12,12,14,14,16,16-hexamethyl-12,14,16-trisilaheptadecane (0.20 g, mmol) in acetone (40 ml) was heated to reflux for 24 h. After cooling, the solvent was removed under reduced pressure, and the solid residue was dissolved in DCM (20 ml) and washed with dilute HCl (1M, 20 ml), brine (20 ml), dried (Mg2SO4) and concentrated. The crude product was purified by flash chromatography on silica gel (3:1 hexane/etoac) to give QL39-5 as a white sold (0.23 g, 83%) Recrystallization from ethanol : 1 H NMR (400 MHz, CDCl3) δ (ppm) 8.45 (s, 2 H), 8.31 (d, J = 8.8 Hz, 2 H), 6.99 (d, J = 8.81 Hz, 2 H), (these are two separate triplets dt, 4 H), (m, 4 H), (m, 20 H), 0.97 (t, J = 7.05 Hz, 3 H), ), 0.49 (br t, 2 H), 0.05 (s,6 H), 0.03 (s, 9 H), 0.00 (s, 6 H), (s, 2 H), (s, 2 H); 13 C NMR (100 MHz, CDCl3) δ , , 151.7, 147.8, 132.3, 129.4, 114.6, 69.2, 68.1, 34.0, 29.57, (several overlapping peaks), 28.0, 26.0, 24.0, 22.3, 18.0, 14.0, 5.7, 4.0, 2.4, 1.5, LRMS (EI) m/z 628 ([M] +, 100), 629, 614(14), 613(25), 412(10), 217 (15), 129 (10); HRMS (EI) m/z calcd for C35H64N2O2Si , found

59 Anal. Calcd for C35H64N2O2Si3: C, 66.85; H, 10.26; N, 4.45; Found: C, 66.74; H, 10.43; N, Hexyloxy-2-[4-(12,12,14,14,16,16-hexamethyl-12,14,16-trisilaheptadecyloxy)phenyl] pyrimidine (QL39-6). To a solution of 3-6 (0.3 g, 0.70 mmol) and 1,1,1,3,3,5,5- heptamethyltrisilane (0.35 g, mmol) in dry toluene (25 ml) was added dropwise Karstedt s catalyst (0.035 ml, mmol) at 0 o C. The mixture was allowed to warm to room temperature and stirred for 48 h. The solvent was removed under reduced pressure and the crude product was purified by silica gel column chromatography (hexane/ethyl acetate 9:1) to give QL39-6 (0.37 g, 82%) as a white solid recrystallization from ethanol: 1 H NMR (400 MHz, CDCl3) δ (ppm) 8.42 (s, 2 H), 8.28 (d, J = 9.0 Hz, 2 H), 6.98 (d, J = 8.8 Hz, 2 H), (these are two separate triplets dt, 4 H), (m, 4 H), (m, 22 H), 0.92 (t, J = 7.0 Hz, 3 H), 0.47 (br t, 2 H), 0.05 (s,6 H), 0.03 (s, 9 H), 0.00 (s, 6 H), (s, 2 H), (s, 2 H); 13 C NMR (100 MHz, CDCl3) δ 160.8, 157.6, 151.0, 143.8, 130.0, 128.9, 114.4, 68.9, 68.0, 33.7, 31.4, (several overlapping peaks),28.76,25.5, 22.5, 18.0, 14.0, 5.7, 4.0, 2.4, 1.4, LRMS (EI) m/z 642 ([M] +, 100), 627 (24), 501(4), 473(6), 425 (6), 129 (3); HRMS (EI) m/z calcd for C36H66N2O2Si , found Anal. Calcd for C36H66N2O2Si3: C, 67.23; H, 10.34; N, 4.36; Found: C, 66.80; H, 10.23; N, Heptyloxy-2-[4-(12,12,14,14,16,16-hexamethyl-12,14,16-trisilaheptadecyloxy)phenyl] pyrimidine (QL39-7). The procedure described for the synthesis of QL39-5 was repeated with 2-7 (0.14 g, mmol) and 1-bromo-12,12,14,14,16,16-hexamethyl-12,14,16- trisilaheptadecane (0.15 g, mmol) to give QL39-7 as a white solid (0.18 g, 82%) rerystallization from ethanol 1 H NMR (400 MHz, CDCl3) δ (ppm) 8.42 (s, 2 H), 8.29 (d, J = 8.8 Hz, 2 H), 6.99 (d, J = 8.8 Hz, 2 H), (these are two separate triplets dt, 4 H),

60 (m, 4 H), (m, 24 H), 0.93 (t, J = 6.9 Hz, 3 H), 0.48 (br t, 2 H), 0.05 (s, 6 H), 0.03 (s, 9 H), 0.00 (s, 6 H), (s, 2 H), (s, 2 H); 13 C NMR (100 MHz, CDCl3) δ 161.1, 157.4, 153.9, 143.8, 132.3, 128.9, 114.4, 69.4, 68.9, 34.0, 31.7, (several overlapping peaks), 25.8, 24.0, 22.6, 18.4, 14.0, 6.0, 4.1, 2.4, 1.4, LRMS (EI) m/z 657 ([M] +, 100), 641 (53), 625 (4), 569(10), 487(14), 431(14), 415 (5); HRMS (EI) m/z calcd for C37H68N2O2Si , found Anal. Calcd for C37H68N2O2Si3: C, 67.66; H, 10.43; N, 4.26; Found: C, 67.71; H, 10.61; N, Octyloxy-2-[4-(12,12,14,14,16,16-hexamethyl-12,14,16-trisilaheptadecyloxy)phenyl] pyrimidine (QL39-8). The procedure described for the synthesis of QL39-5 was repeated with 2-8 (0.15 g, mmol) and 1-bromo-12,12,14,14,16,16-hexamethyl-12,14,16- trisilaheptadecane (0.19 g, mmol) to give QL39-8 as a white solid (0.23 g, 82%) recrystallization from ethanol: 1 H NMR (400 MHz, CDCl3) δ (ppm) 8.43 (s, 2 H), 8.28 (d, J = 8.8 Hz, 2 H), 6.98 (d, J = 8.8 Hz, 2 H), 4.06 (these are two separate triplets dt, 4 H), (m, 4 H), (m, 26 H), 0.92 (t, J = 7.0 Hz, 3 H), ), 0.47 (t, 2 H), 0.05 (s, 6 H), 0.03 (s, 9 H), 0.00 (s, 6 H), (s, 2 H), (s, 2 H); 13 C NMR (100 MHz, CDCl3) δ 160.0, 158.5, 151.1, 147.3, 137.9, 129.1, 114.5, 69.6, 69.0, 33.7, 31.7, 30.0, 29.57, (several overlapping peaks), 25.7, 23.9, 22.5, 18.0, 12.8, 5.8, 4.0, 2.4, 1.4, -0.4 LRMS (EI) m/z 670 ([M] +, 100), 453 (22), 217(44), 188(49), 145 (20), 129 (71); HRMS (EI) m/z calcd for C38H70N2O2Si , found Anal. Calcd for C38H70N2O2Si3: C, 68.03; H, 10.52; N, 4.17; Found: C, 67.80; H, 10.15; N, Nonyloxy-2-[4-(12,12,14,14,16,16-hexamethyl-12,14,16-trisilaheptadecyloxy)phenyl] pyrimidine (QL39-9). The procedure described for the synthesis of QL39-5 was repeated with 46

61 2-9 (0.2 g, mmol) and 1-bromo-12,12,14,14,16,16-hexamethyl-12,14,16- trisilaheptadecane (0.2 g, mmol) to give QL39-9 as a white solid (0.27 g, 90%) recrystallization from ethanol: 1 H NMR (400 MHz, CDCl3) δ (ppm) 8.42 (s, 2 H), 8.29 (d, J = 8.8 Hz, 2 H), 6.99 (d, J = 8.8 Hz, 2 H), 4.10 (these are two separate triplets dt, 4 H), (m, 4 H), (m, 28 H), 0.91 (t, J = 7.0 Hz, 3 H), ), 0.48 (t, 2 H), 0.05 (s, 6 H), 0.03 (s, 9 H), 0.00 (s, 6 H), (s, 2 H), (s, 2 H); 13 C NMR (100 MHz, CDCl3) δ 162.9, 157.6, 150.5, 143.8, 133.2, 128.9, 114.4, 68.64, 68.09, 33.7, 31.8, (several overlapping peaks), 25.8, 23.9, 22.6, 18.0, 13.8, 5.5, 4.0, 2.4, 1.4, -0.4 LRMS (EI) m/z 684 ([M] +, 100), 640 (21), 386(6), 327(7), 145 (7); HRMS (EI) m/z calcd for C39H72N2O2Si , found Anal. Calcd for C39H72N2O2Si3: C, 68.39; H, 10.59; N, 4.09; Found: C, 68.09; H, 10.75; N, Decyloxy-2-[4-(12,12,14,14,16,16-hexamethyl-12,14,16-trisilaheptadecyloxy)phenyl] pyrimidine (QL39-10). The procedure described for the synthesis of QL39-5 was repeated with 2-10 (0.15 g, mmol) and 1-bromo-12,12,14,14,16,16-hexamethyl-12,14,16- trisilaheptadecane (0.137 g, mmol) to give QL39-10 as a white solid (0.17 g, 80%) recrystallization from ethanol: 1 H NMR (400 MHz CDCl3) δ (ppm) 8.42 (s, 2 H), 8.29 (d, J = 8.8 Hz, 2 H), 6.99 (d, J = 8.8 Hz, 2 H), 4.10 (these are two separate triplets dt, 4 H), (m, 4 H), (m, 30 H), 0.91 (t, J = 6.8 Hz, 3 H), ), 0.48 (t, 2 H), 0.05 (s, 6 H), 0.03 (s, 9 H), 0.00 (s, 6 H), (s, 2 H), (s, 2 H); 13 C NMR (100 MHz, CDCl3) δ 161.5, 159.7, 151.1, 147.3, 132.3, 129.1, 114.5, 69.6, 69.0, 33.7, 31.7, 30.0, 29.57, (several overlapping peaks), 27.7, 23.9, 22.5, 18.0, 12.8, 5.8, 4.0, 2.4, 1.4, -0.4 LRMS (EI) m/z 698 ([M] +, 100), 683 (22), 481(14), 188(15), 129 (18); HRMS (EI) m/z calcd for C40H74N2O2Si , found

62 Anal. Calcd for C40H74N2O2Si3: C, 68.74; H, 10.67; N, 4.01; Found: C, 69.06; H, 10.70; N, Synthesis of QL40-n Liquid Crystal Dimers Scheme1 Reagent and conditions: (a) K2CO3, methyl ethyl ketone, reflux, overnight. 1,27-Bis-[4-(5-pentyloxypyrimidin-2-yl)phenoxy]-12,12,14,14,16,16-hexamethyl- 12,14,16-trisilaheptacosane (QL40-5). A mixture of 2-5 (0.5 g, 1.93 mmol), K2CO3 (0.98 g, 7.09 mmol) and 1,27-dibromo-12,12,14,14,16,16-hexamethyl-12,14,16-trisilaheptacosane (0.432 g, mmol) in methyl ethyl ketone (40 ml) was heated to reflux for 24 h. After cooling, the solvent was removed under reduced pressure, and the solid residue was dissolved in DCM (20 ml) and washed with dilute HCl (1 M, 20 ml), brine (20 ml), dried (MgSO4) and concentrated. The crude product was purified by flash chromatography on silica gel (3:1 hexane/etoac) to give QL40-5 as a white solid (0.47 g, 71%) recrystallization from ethanol 1 H NMR (400 MHz, CDCl3) δ (ppm) 8.44 (s, 4 H), 8.28 (d, J = 8.8 Hz, 4 H), 6.99 (d, J = 8.8 Hz, 4 H), (these are two separate triplets dt, 8 H), (m, 8 H), (m, 40 H), 0.94 (t, J = 7.0 Hz, 6 H), ), 0.47 (t, 4 H), 0.05 (s, 6 H), 0.00 (s, 12 H), (s, 4 H); 13 C NMR (100 MHz, CDCl3) δ , , 151.2, 146.2, 132.3, 129.0, 114.4, 69.2, 68.4, 34.6, 29.91, (several overlapping peaks), 28.0, 25.0, 24.0, 22.3, 18.0, 14.0, 48

63 4.0, 2.5, -0.4 LRMS (ESI) m/z 1025 ([M+1] +,18), ), 1009 (100), 955 (26), 939 (13),767 (27), 751 (37), 735 (23), 597 (38) 541 (21), 525 (12); (HRMS (EIS) m/z calcd for C60H100N4O4Si , found Anal. Calcd for C60H100N4O4Si3: C, 70.21; H, 9.92; N, 5.46; Found: C, 69.96; H, 9.81; N, ,27-Bis-[4-(5-hexyloxypyrimidin-2-yl)phenoxy]-12,12,14,14,16,16-hexamethyl-12,14,16- trisilaheptacosane (QL40-6). The procedure described for the synthesis of QL40-5 was repeated with 2-6 (0.25 g, 0.98 mmol) and 1,27-dibromo-12,12,14,14,16,16-hexamethyl- 12,14,16-trisilaheptacosane (0.2 g, 0.30 mmol). The crude product was purified by flash chromatography on silica gel (3:1 hexane/etoac) to give QL40-6 as a white solid (0.20 g, 51%) recrystallization from ethanol: 1 H NMR (400 MHz, CDCl3) δ (ppm) 8.42 (s, 4 H), 8.28 (d, J = 9.0 Hz, 4 H), 6.98 (d, J = 8.8 Hz, 4 H), (these are two separate triplets dt, 8 H), (m, 8 H), (m, 44 H), 0.92 (t, J = 7.0 Hz, 6 H), ), 0.47 (t, 4 H), 0.05 (s, 6 H), 0.00 (s, 12 H), (s, 4 H); 13 C NMR (100 MHz, CDCl3) δ 160.7, 157.0, 151.0, 143.8, 129.9, 128.9, 114.4, 68.95, 68.09, 33.7, 31.4, (several overlapping peaks), 28.7, 26.0, 25.5, 23.9, 22.5, 18.0, 13.9, 4.1, 2.5, LRMS (ESI) m/z 1053 ([M+1] +, 100), 1038 (30), 1037 (100), 696 (23), 781 (23),765 (33), 611 (32) HRMS (EIS) m/z calcd for C62H104N4O4Si , found Anal. Calcd for C62H105N4O4Si3: C, 70.69; H, 5.39; N, 9.95; Found: C, H, 5.27; N, ,27-Bis-[4-(5-heptyloxypyrimidin-2-yl)phenoxy]-12,12,14,14,16,16-hexamethyl- 12,14,16-trisilaheptacosane (QL40-7). The procedure described for the synthesis of QL40-7 was repeated with 2-7 (0.25 g, mmol) and 1,27-dibromo-12,12,14,14,16,16-hexamethyl- 12,14,16-trisilaheptacosane (0.2 g, 0.29 mmol) The crude product was purified by flash chromatography on silica gel (3:1 hexane/etoac) to give QL40-7 as a white solid (0.29 g, 90%) recrystallization from ethanol: 1 H NMR (400 MHz, CDCl3) δ (ppm) 8.42 (s, 4 H),

64 (d, J = 8.8 Hz, 4 H), 6.98 (d, J = 8.8 Hz, 4 H), (these are two separate triplets dt, 8 H), (m, 8 H), (m, 48 H), 0.93 (t, J = 7.0 Hz, 6 H), 0.48 (t, 4 H), 0.05 (s, 6 H), 0.00 (s, 12 H), (s, 4 H); 13 C NMR (100 MHz, CDCl3) δ 160.7, 157.0, 151.0, 143.8, 130.0, 128.9, 114.4, 68.95, 68.09, 33.7, 31.4, 29.62, (several overlapping peaks), 26.0, 25.5, 23.9, 22.5, 18.0, 13.9, 4.1, 2.5, LRMS (ESI) m/z 1081 ([M+1] +, 100), 1065 (2), 989 HRMS (EIS) m/z calcd for C64H108N4O4Si , found Anal. Calcd for C64H108N4O4Si3: C, 71.08; H, 10.06; N, 5.18; Found: C, 71.02; H, 10, 04; N, ,27-Bis-[4-(5-octyloxypyrimidin-2-yl)phenoxy]-12,12,14,14,16,16-hexamethyl-12,14,16- trisilaheptacosane (QL40-8). The procedure described for the synthesis of QL40-5 was repeated with 2-8 (0.41 g, 1.33 mmol) and 1,27-dibromo-12,12,14,14,16,16-hexamethyl- 12,14,16-trisilaheptacosane (0.305 g, mmol) The crude product was purified by flash chromatography on silica gel (3:1 hexane/etoac) to give QL40-8 as a white solid (0.45 g, 67%) recrystallization from ethanol: 1 H NMR (400 MHz, CDCl3) δ (ppm) 8.42 (s, 4 H), 8.28 (d, J = 9.0 Hz, 4H), 6.98 (d, J = 8.8 Hz, 4 H), (these are two separate triplets dt, 8 H), (m, 8 H), (m, 52 H), 0.92 (t, J = 7.0 Hz, 6 H), ), 0.47 (t, 4 H), 0.05 (s, 6 H), 0.00 (s, 12 H), (s, 4 H); 13 C NMR (100 MHz, CDCl3) δ 160.7, 157.0, 151.0, 143.8, 129.9, 128.9, 114.4, 68.9, 68.0, 33.7, 31.4, 29.62, (several overlapping peaks), 26.0, 25.5, 23.9, 22.5, 18.0, 13.9, 4.1, 2.5, LRMS (ESI) m/z 1110 ([M+1] +,18) 1094 (94), 1093 (100), 998 (14), 997 (17), 809 (19), 793 (19), 639 (21), 583 (20) HRMS (EIS) m/z calcd for C66H113N4O4Si , found Anal. Calcd for C66H113N4O4Si3: C, 71.36; H, 10.25; N, 5.04; Found: C, 71.74; H, 10, 24; N,

65 1,27-Bis-[4-(5-nonyloxypyrimidin-2-yl)phenoxy]-12,12,14,14,16,16-hexamethyl-12,14,16- trisilaheptacosane (QL40-9). The procedure described for the synthesis of QL40-5 was repeated with 2-9 (0.21 g, mmol) and 1,27-dibromo-12,12,14,14,16,16-hexamethyl- 12,14,16-trisilaheptacosane (0.15 g, mmol) The crude product was purified by flash chromatography on silica gel (3:1 hexane/etoac) to give QL40-9 as a white solid (0.17 g, 68%) recrystallization from ethanol: 1 H NMR (400 MHz, CDCl3) δ (ppm) 8.42 (s, 4 H), 8.28 (d, J = 9.1 Hz, 4 H), 6.98 (d, J = 9.1 Hz, 4 H), (these are two separate triplets dt, 8 H), (m, 8 H), (m, 56 H), 0.92 (t, J = 6.9 Hz, 6 H), ), 0.47 (t, 4 H), 0.05 (s, 6 H), 0.00 (s, 12 H), (s, 4 H); 13 C NMR (100 MHz, CDCl3) δ , , , , , , , 68.93, 68.08, 33.72, 31.85, (several overlapping peaks), 26.06, 25.52, 23.98, 22.66, 19.18, 14.11, 4.10, 2.53, LRMS (ESI) m/z 1137 ([M+1] +,100), 1021 (20), 1011 (3), 919 (7), 635 (2),597 (2) HRMS (EIS) m/z calcd for C68H116N4O4Si , found Anal. Calcd for C68H116N4O4Si3: C, 71.77; H, 10.27; N, 4.92; Found: C, 72.02; H, 10, 22; N, ,27-Bis-[4-(5-decyloxypyrimidin-2-yl)phenoxy]-12,12,14,14,16,16-hexamethyl-12,14,16- trisilaheptacosane (QL40-10). The procedure described for the synthesis of QL40-5 was repeated with 2-10 (0.21 g, mmol) and 1,27-dibromo-12,12,14,14,16,16-hexamethyl- 12,14,16-trisilaheptacosane (0.15 g, mmol) The crude product was purified by flash chromatography on silica gel (3:1 hexane/etoac) to give QL40-10 as a white solid (0.30 g, 78%) recrystallization from ethanol: 1 H NMR (400 MHz, CDCl3) δ (ppm) 8.42 (s, 4 H), 8.28 (d, J = 7. 9 Hz, 4H), 6.98 (d, J = 8. 1 Hz, 4 H), (these are two separate triplets dt, 8 H), (m, 8 H), (m, 60 H), 0.92 (t, J = 6. 4 Hz, 6 H), ), 0.47 (t, 4 H), 0.05 (s, 6 H), 0.00 (s, 12 H), (s, 4 H): 13 C NMR (100 MHz, CDCl3) δ , , , 51

66 143.83, , , , 68.93, 68.08, 33.72, 31.85, (several overlapping peaks), 26.06, 25.52, 23.98, 22.66, 19.18, 14.11, 4.10, 2.53, LRMS (ESI) m/z 1164 (8), 1149 (90), 1148 (100), 1125 (20), 1124 (31), 938 (35), 922 (17), 677 (20), 611 (12) HRMS (EIS) m/z calcd for C70H120N4O4Si , found Anal. Calcd for C70H120N4O4Si3: C, 72.11; H, 10.37; N, 4.81; Found: C, 71.98; H, 30, 04; N,

67 3.2 Reference 1- Zhang, Y.; O'Callaghan, M. J.; Walker, C.; Baumeister, U.; Tschierske, C. Chem. Mater. 2010, 22,

68 Chapter 4. Conclusions and Future Work The first goal of this thesis was to test a hypothesis regarding the effect of carbosilane nanosegregation on the de Vries-like properties of smectic liquid crystals, based on the previous findings of the Lemieux group. Those findings indicated that correlation with carbosilane end-group mesogens may produce a significant amount of free volume in the hydrocarbon sub-layer. An additional goal of this thesis was further understanding of the origin of de Vries-like behavior in carbosilane end-group mesogens. In this thesis, two new homologous series of carbosilane liquid-crystal dimers (QL40- n) and monomers (QL39-n) with tricarbosilane spacers and end-group, respectively were synthesized. The POM and X-ray data indicate that, in QL40-n series, orthogonal SmA and SmX phases are formed, whereas QL39-n form a tilted SmC phase only. The fact that the SmA phase is not observed in QL39-n suggests that the dimers and monomers have different properties. The evidence suggests that the carbosilane segment in the dimers QL40-n has a smaller cross-section on time average than in the monomersql39-n, which is consistent with our hypothesis. Further studies will seek to validate these results by restoring the de Vries-like behavior in the QL41-n series using a laterally bulky tricarbosilane spacer in which R = CH2SiMe3. QL41-n 54

69 Appendix 1. 1 H NMR Spectra of Novel Liquid Crystals SH esp Normalized Intensity Chemical Shift (ppm) Figure A1-1: 400 MHz 1 H NMR spectrum of QL39-5 Figure A1-2: 400 MHz 1 H NMR spectrum of QL

70 SH0C esp Normalized Intensity Chemical Shift (ppm) Figure A1-3: 400 MHz 1 H NMR spectrum of QL39-7 SH esp Normalized Intensity Chemical Shift (ppm) Figure A1-4: 400 MHz 1 H NMR spectrum of QL

71 SH0C9 monmer.010.esp Normalized Intensity Chemical Shift (ppm) Figure A1-5: 400 MHz 1 H NMR spectrum of QL39-9 SH0C10 monmer.010.esp Normalized Intensity Chemical Shift (ppm) Figure A1-6: 400 MHz 1 H NMR spectrum of QL

72 SH041-A.010.esp Normalized Intensity Chemical Shift (ppm) Figure A1-7: 400 MHz 1 H NMR spectrum of QL40-5 SH esp Normalized Intensity Chemical Shift (ppm) Figure A1-8: 400 MHz 1 H NMR spectrum of QL

73 SH esp Normalized Intensity Chemical Shift (ppm) SH038C8d.010.esp Figure A1-9: 400 MHz 1 H NMR spectrum of QL Normalized Intensity Chemical Shift (ppm) Figure A1-10: 400 MHz 1 H NMR spectrum of QL

74 .010.esp Normalized Intensity Chemical Shift (ppm) Figure A1-11: 400 MHz 1 H NMR spectrum of QL40-9 SHc10crbon.010.esp Normalized Intensity Chemical Shift (ppm) Figure A1-12: 400 MHz 1 H NMR spectrum of QL

75 Appendix 2. DSC Profiles of Liquid Crystals Figure A2-1: DSC profile for compound QL39-5 taken at a scan rate of 5K/min. Figure A2-2: DSC profile for compound QL39-6 taken at a scan rate of 5K/min. 61

76 Figure A2-3: DSC profile for compound QL39-7 taken at a scan rate of 5K/min. Figure A2-4: DSC profile for compound QL39-8 taken at a scan rate of 5K/min. 62

77 Figure A2-5: DSC profile for compound QL39-9 taken at a scan rate of 5K/min. Figure A2-6: DSC profile for compound QL39-10 taken at a scan rate of 5K/min. 63

78 Figure A2-7: DSC profile for compound QL40-5 taken at a scan rate of 5K/min. Figure A2-8: DSC profile for compound QL40-6 taken at a scan rate of 5K/min. 64

79 Figure A2-9: DSC profile for compound QL40-7 taken at a scan rate of 5K/min. Figure A2-10: DSC profile for compound QL40-8 taken at a scan rate of 5K/min. 65

80 Figure A2-11: DSC profile for compound QL40-9 taken at a scan rate of 5K/min. Figure A2-12: DSC profile for compound QL40-10 taken at a scan rate of 5K/min. 66

81 Appendix 3. Textures of Liquid Crystals by Polarized Microscopy Figure A3-1: Textures of compound QL39-5 observed by polarized microscopy on cooling: in the SmC phase at 42 C. Figure A3-2: Textures of compound QL39-6 observed by polarized microscopy on cooling: in the SmC phase at 70 C. Figure A3-3: Textures of compound QL39-7 observed by polarized microscopy on cooling: in the SmC phase at 68 C. 67

82 Figure A3-4: Textures of compound QL39-8 observed by polarized microscopy on cooling: in the SmC phase at 69 C. Figure A3-5: Textures of compound QL39-9 observed by polarized microscopy on cooling: in the SmC phase at 66 C. Figure A3-6: Textures of compound QL39-10 observed by polarized microscopy on cooling: in the SmC phase at 80 C. 68

83 Figure A3-7: Textures of compound QL40-5 observed by polarized microscopy on cooling in the SmA at 85 C on cooling (left) and the SmX phase at 70 C (right) (200X Magnification). Figure A3-8: Textures of compound QL40-6 observed by polarized microscopy on cooling: in the SmA phase at 91 C (left) and in the SmX phase at 74 C (right) (200X Magnification). Figure A3-9: Textures of compound QL40-7 observed by polarized microscopy on cooling: in the SmA phase at 90 C (left) and in the interfere SmX phase at 75 C (right) (200X Magnification). 69

84 Figure A3-10: Textures of compound QL40-8 observed by polarized microscopy on cooling: in the SmA phase at 95 C (left) and in the SmX phase at 93 C (right) (200X Magnification). Figure A3-11: Textures of compound QL40-9 observed by polarized microscopy on cooling: in the SmA phase and the interfere SmA phase at 85 C (200X Magnification). Figure A3-12: Textures of compound QL40-10 observed by polarized microscopy on cooling: in the SmA phase and the interfere SmA phase at 90 C (200X Magnification). 70